Dilution is utilized in analytical laboratories for various purposes, including preparation of calibration standards, to bring sample concentrations within instrumental working ranges, and to reduce matrix effects. In a sample introduction system, it is often necessary to dilute a solution prior to analysis by an analyzer such as an Inductively Coupled Plasma Mass Spectrometer (ICP-MS). Dilution may be necessary for a sample that is out of range of the analyzer, such as a high concentration analyte, or to correct a quality control error. Dilution may be accomplished off-line, in a sample preparation area, or online at the ICP-MS. On-line dilution may be advantageous as it minimizes the steps required for preparation of a sample for analysis. Disadvantageously, the need to dilute a solution prior to analysis may be a time-consuming operation. As a result, several techniques providing automated on-line sample dilution have been developed. However, dilution with all of these techniques is generally accomplished by varying the pump speeds of the pumps to increase or decrease the ratio of the flow rates of the introduced sample and the diluent to be mixed with the sample. For example, the relative speed of two or more pumps each carrying a solution may be increased and decreased with respect to one another depending on a selected dilution factor. This constant variation of pump speed of two or more lines carrying a diluent and a sample creates inefficiency in sample analysis as it requires constant monitoring and calibration of pump equipment, flow rates and diluent ratios. Furthermore, many of these techniques require a vacant line to transfer a diluted sample to an analyzer.
Consequently, it is desirable to provide on-line constant flow sample dilution that does not require a change in pump speed to vary sample to diluent ratio when diluting a sample for analysis.